What is it?

Citrix has introduced a feature for cloud deployments which causes zones in a XenDesktop site to be automatically synchronized with the Cloud Resource Locations associated with the site.

Zones are used to arrange the site resources (catalogs, hypervisor connections, application and user home zones, etc.) so users connecting to the site from one location get access to ‘local’ applications. Performance is much better when connecting to somewhere on the same side of the country, or even the same side of the world.

A zone needs a Cloud Connector — sometimes called an Edge Server — to communicate between the Citrix managed Controller (DDC) in the cloud and the customer-managed-and-owned servers and desktops located on premise or in a private cloud. When multiple Resource Locations and Connectors are involved the site must be configured correctly in order to behave as intended.

Why are we introducing this?

Up until now, many cloud customers have had a single zone site using the default settings. It looks something like this:

Fig. 1 Default site configuration.

This XD Site has not had a zone created and the Connector, CC-1, has been placed in the Primary or Initial Zone. All resources (the hypervisor connections, catalogs, etc.) are also located in the Primary Zone. This typical site works because there is only one zone and everything, including the Connector is in the same zone.

However, going forward, as a best practice, the Primary zone should only contain the DDC and database and all other resources should exist in one or more separate zones.

Below is an example of what a single-zone site should look like, with a (recommended) second Connector CC-2 added:

Fig. 2 Correctly configured site.

This site is effectively the same as the previous example in Fig. 1, but is correctly configured so the Connector and all resources that use it are located in the secondary zone which is tied to the Resource Location. If additional Connectors [CC-2] are added to the same Resource Location they should also be added to “My Zone 1” to provide redundancy. In this case, all Connectors in the zone point to the same set of resources and it doesn’t matter which Connector is used to carry out any operation.

Once a customer decides that they need additional zones, for example to cover East coast and West coast or New York and London sites, and one or more secondary zones are added to the site things can get more complicated to administer. Studio tries to help administrators by attempting to keep a one-to-one mapping between secondary zones and the Cloud Resource Locations and linking them together, but using the PowerShell SDK directly can result in a mismatch of zones to Resource Locations.

Unfortunately what has happened with some sites is that Connectors have been added to the Resource Location(s), but not placed into the correct zone, or subsequently moved to a different zone. If additional zones and Resource Locations are added it can get quite messy with Connectors from different Resource Locations being in the same zone. If a zone doesn’t exist in the site for the Resource Location when the Connector is added, the Connector is added to the Primary Zone and should then be moved to the correct zone when it is created. However if it isn’t moved for any reason, or it’s moved to the wrong zone, ‘bad things’ can happen… It’s random which Connector is used to connect to the resources and if these Resource Locations do reflect different geographic locations it can result in some poor performance or session launch failures if the Connector can’t see the resource in the ‘other’ location. When using Gateway as a Service performance can be degraded if the ‘wrong’ Connector is selected when connecting to VDAs sending network traffic to remote rather than local Resource Locations.

An example of a badly configured site which has 2 Resource Locations, each with 2 edge connectors (a and b) is shown below:

Fig3. Badly configured site

In the above site, Zone 1 is fine, but Zone 2 has Connectors from multiple Resource Locations which can cause intermittent errors depending on which Connector is used for any particular operation. If CC-1a, which belongs with Resource Location 1, is used to try to launch an application or provision a new server for a catalog in Zone 2, then it will be talking to resources through the Connector in Zone 1 which may or may not able to see the resources in Zone 2. CC-1a should be moved into Zone 1. In addition, the CC-2a in the Primary Zone should be moved into Zone 2 as should the resources in the Primary Zone. [Technically the resources could be moved into either Zone 1 or Zone 2, but as they are currently using a Connector in Zone 2 that seems the best Zone to use.]

How does this feature help?

To prevent this situation occurring, Citrix is introducing this new feature which provides the customer with improved robustness and automatic configuration, but does not provide any new facilities. It removes the ability to create or delete zones and move Connectors out of the correct zone whether using Studio or the SDK, removing the ability to misconfigure zones. All zones will be created and deleted automatically. Creating a new Resource Location and adding a Connector to it will result in a new zone being added to the site with the same name as the Resource Location within a few minutes. It will not be possible to delete or rename the zone through Studio, nor will it be possible to move Connectors out of the correct zone. Renaming the zone should be done by renaming the Resource Location. If a zone is no longer required, delete the Connectors and the Resource Location in the cloud – the zone will be deleted from the XD site (but only once it is empty). Any resources in the zone should be moved into another suitable zone or deleted as required.

This should ensure all zones have the correct Connectors and remove the intermittent errors that have been seen when sessions are launched from a catalog which is in a zone with Connectors from multiple Resource Locations or even no Connectors at all.

Impact & customer actions

All new customers will have this feature enabled so zones and Connectors will be managed automatically as described above. Existing customers with the ‘simple’ site configuration shown in Figure 1, or a correctly configured site where all Connectors and resources are already positioned in the correct zones shouldn’t see any real difference, though zones may get their names changed to match that of the Resource Location. If desired, change the Resource Location name to match the preferred zone name before or after the feature is enabled.

There are some sites that could be badly configured however in these cases don’t worry as the Citrix Cloud team will contact you to resolve any issues before feature is enabled.